Multicast and Router mode

[Guus Sliepen]

On Mon, Feb 25, 2013 at 06:12:13PM +0000, Mike C wrote:

> I have seen http://www.tinc-vpn.org/pipermail/tinc-devel/2010-October/000473.html
> and so tried out for myself to see if multicast would work in tinc
> using routing mode. I'm using tinc 1.0.19. My test involved sending a
> ping out on 224.1.1.1 (as 224.0.0.0/24 is a special case), and while I
> could see the traffic reaching the other tinc daemons, it never seemed
> to go out to the local network. Turning on debugging, I could see the
> packet reach the other site, but it doesn't get broadcast out onto the
> network (wireshark shows nothing; I'm not expected any machines to
> respond to the ping, it's just an easy way to send out something
> multicast).

That is just the way Linux works. It doesn't forward multicast traffic by
default. You have to have multicast routes to all interfaces you want multicast
on, enable IP forwarding, and you might also need to run a multicast routing
daemon (pimd, smcroute, igmpproxy, et cetera). I haven't done multicast stuff
for a long time, I'm afraid I cannot help you here.

> # ip route add 224.1.1.1/16 dev vpn

I don't think it is a good idea to assign a multicast IP address directly to an
interface. In principle, hosts which have multicast configured correctly should
respond to ping packets to 224.0.0.1.

> Looking at the code corresponding to "Broadcast packet", which from
> what I can tell, sends the packet to other nodes, as well as sends it
> to itself: send_packet(myself, packet);, however nothing shows up on
> wireshark.

You should at least see it on the VPN interface. However, that is as far as
tinc's responsibilities go.

-- 
Met vriendelijke groet / with kind regards,
     Guus Sliepen <guus at tinc-vpn.org>
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